reverse osmosis needs a certain water pressure to work, i believe its around 50 psi. I would look into it and make sure you have enough water pressure first. It works by forcing water through an impermeable membrane, which means, water goes through it, and solids dont, but you need enough pressure to force the water through the membrane. They make an RO unit with a pump, not sure how it works, but supposedly it makes the process more efficient so you dont need as much pressure. To answer your question, yes you can hook it up to a hose if it has the correct pressure.

Never heard of dry ice in the resi, might not be a bad thing, but not a good thing for sure.

Pretty sure roots breath oxygen. Thats why you want to oxygenate your water with air stones and h202.

Leaves breathe c02, thats how photosynthesis works, the plant uses the C to make CH2O, which is a carbohydrate, and the 02 is released into the atmosphere as oxygen. Thats super basic, but you get the point.